I have a new switch bar (the one with the hazard, hill control switch etc) the reason being that I wanted one with the parking sensor switch.
Are these switches easy to replace or is it a job for my garage?

Assuming it's a facelift, it's an absolute doddle.
I would strongly recommend a plastic trim removal tool to help lift the flat panel between the centre vents / below the nav screen.
It also helps to lift the the top of dash speaker grill. This is clipped down with three spring clips which like to fire off and vanish into the car, so go slow. I think there are then 6 torx screws to release the centre console, then pull the whole thing forward. Two more screws to hold the switches in. Easy.